Glow discharge apparatus having a stacked array of magnets



April 1963 H. E. AINE 3,377,495

GLOW DISCHARGE APPARATUS HAVING A STACKED ARRAY OF MAGNETS Filed June 17, 1965 INVENTOR HARRY E. AINE BY M M A ATTORNEY United States Patent 3,377,495 GLOW DISCHARGE APPARATUS HAVING A STACKED ARRAY OF MAGNETS Harry E. Aine, Palo Alto, Caliii, assignor to Varian Associates, Palo Alto, Calif., a corporation of California Filed June 17, 1965, Ser. No. 464,813 8 Claims. (Cl. 313-161) ABSTRACT OF THE DISCLOSURE This invention relates to vacuum apparatus and particularly to magnetically confined glow discharge apparatus. While not limited thereto, the invention has utility as a vacuum pump apparatus in providing uncontaminated high vacuum as required in, for example, thin film deposition, high altitude simulation, friction studies, semiconductor processing, electron tube processing and high frequency particle accelerators.

In my copending application Ser. No. 383,677, filed July 20, 1964 and assigned to the same assignee as the present invention, there is disclosed a magnetically confined glow discharge apparatus comprising: an evacuable envelope; magnet means disposed within the envelope including a pair of permanent magnets, each having a north pole N at one end and a south pole S at an opposite end, arranged in a stack such that adjacent magnets in the stack are polarized in opposite directions; pole pieces extending outwardly from the poles of the magnet means; and glow discharge elements including spaced-apart anode and cathode members disposed between the pole pieces. By so doing the leakage field across each magnet goes into its own useful gap while the leakage field which surrounds one magnet goes into the useful magnet gap of the adjacent magnet.

The present invention involves a magnetically confined glow discharge apparatus which, while dependent on the basic principles of the aforementioned application, contemplates many advantages not heretofore achieved; in particular, it permits the use of less expensive magnetic material and bakeout to much higher temperatures.

Accordingly, it is the principal object of the present invention to provide a magnetically confined glow discharge pump apparatus in which the magnetic material is used eificiently, the mechanical design is simplified, the pump performance is improved and, in addition, less expensive magnetic material and bakeout to much higher temperatures are permitted.

Briefly stated, in accordance with one teaching of the present invention there is disclosed a magnetically confined glow discharge apparatus for evacuating a region of space including: a gas impervious tube having a walled internal bore therein adapted and arranged to extend into the region to be evacuated and including a plurality of magnetic pole piece members and a nonmagnetic spacer segment located between the pole piece members and serving to space the pole pieces one from another; magnet means telescopically received within the tube, including at least one pair of permanent magnets, each having a north pole at one end and a south pole at an opposite end, and

arranged in a stack such that adjacent magnets in the stack are polarized in opposite directions; a plurality of pole piece discs disposed within the tube in intimate contact With the walls, located between the permanent magnets in registry with the pole piece mambers and serving to space the magnet magnets and provide a low reluctance path to the pole piece members; and an anode member adapted to initiate and maintain a glow discharge upon energization thereof, located within the region of space to be evacuated between portions of the pole piece members extending outwardly of the tube. By so doing the permanent magnets can be readily removed during bakeout without destroying the vacuum integrity of the region of space. This construction also permits the use of less expensive magnetic material such as the ferrites which generally are unacceptable for use inside the region of space being evacuated due to their porosity and outgassing, and which cannot withstand bakeout temperatures, typically on the order of 400 C. and higher.

One feature of the present invention is the provision in a magnetically confined glow discharge apparatus containing a region of space to be evacuated of a gas impervious tube having a walled, internal bore therein adapted and arranged to extend into the region of space to be evacuated and including a plurality of magnetic, pole piece segments separated by a non-magnetic spacer segment located between the pole piece segments and serving to space the pole piece segments one from another.

Another feature of the present invention is the provision in a magnetically confined glow discharge apparatus of the above type of magnet means telescopically received within the tube including at least one pair of permanent magnets, each having a north pole at one end and a south pole at an opposite end, arranged in a stack such that adjacent magnets in the stack are polarized in opposite directions, the poles of the magnets being disposed adjacent the magnetic pole piece segments.

Still another feature of the present invention is the provision in a magnetically confined glow discharge apparatus of the above type of pole piece discs disposed within the two in intimated contact with the walled bore, located between the permanent magnets in registry with the magnetic pole piece segments.

These and other features and objects of the present invention and a further understanding may be had by referring to the following description and claims taken in conjunction with the following drawing in which: 7

FIG, 1 is a schematic block diagram depicting a typical evacuation system utilizing a novel magnetically confined glow discharge vacuum pump apparatus constructed in accordance with the teachings of the present invention.

FIG. 2 is a longitudinal sectional view partially broken away of an improved magnetically confined glow discharge vacuum pump apparatus of the present invention utilizing a circular geomery;

FIG. 3 is a cross-sectional view taken along the lines 33 of FIG. 2, and

FIG. 4 is a fragmentary, cross-sectional view of an alternate embodiment of the present invention.

Referring now to FIG. 1 there is shown in schematic block diagram form the improved magnetically confined glow discharge vacuum pump apparatus of the present invention as utilized for evacuating a given structure. Specifically, the vacuum pump 11 is connected by means of a conduit and through a first high vacuum joint 12 containing a pair of ultra-high vacuum flanges and a metal gasket (not shown) to a structure 13 which it is desired to evacuate. A vacuum sorption pump 14 is also connected to the structure 13 to be evacuated by means of conduits and through a pair of high vacuum joints 15, 16 and a high vacuum valve 17. Frequently, a mechanical pump is used instead of the vacuum sorption pump 3 14. To evacuate the structure, the vacuum sorption pump 14 is immersed in a refrigerating liquid 18, as, for eX- ample, liquid nitrogen, held in an open vessel 19. Gas molecules are sorbed by the pump 14 from the structure 13 serving to reduce the pressure within the structure 13 to between and 20 or lower microns at which point the valve 17 is closed and the vacuum pump 11 started.

The pump 11 is supplied with operating potentials from a source 20 as, for example, a 60-cycle power line via a transformer 21. The secondary of the transformer 20 is provided with a rectifier 22 and a shunting smoothing capacitor 23 whereby a DC. potential may be applied between anode and the grounded cathode members of the vacuum pump 11, which pump will be more fully described below.

Referring now to FIGS. 2-3, there is shown an embodiment of the present invention employing a circular geometry. Specifically, pump 11 includes a cylindrical, evacuable envelope 24 made of, for example, 304 stainless steel A2" thick. The ends of envelope 24 are closed off by an apertured top plate 25, as of stainless steel, and an apertured bottom plate 26 of magnetic material such as soft iron, both fixed to envelope 24 by, for example, Heliarc inert atmosphere arc Welding.

An exhaust tubulation 27, as of 304 stainless steel, is carried from apertured top plate 25 and communicates with the interior of envelope 24. A vacuum sealing flange 28, as of stainless steel, is carried from the end of tubing 27 in a vacuum tight manner and is adapted for mating with another sealing flange, which flanges serve to compress a copper gasket (not shown) therebetween so as to form the vacuum tight joint 12.

Centered about the opening in bottom plate 26 and extending axially inwardly therefrom is a tubular channel or re-entrant finger 29. The finger 29 is defined by a stack of alternating non-magnetic tubular segments 30 such as stainless steel and annular magnetic pole piece members 31, such as soft iron, brazed together, with the outermost segment 30' brazed to bottom plate 26, and the innermost segment 30 brazed to a circular magnetic disc 31' to form with envelope 24 a unitary vacuum structure. Alternatively, the entire finger 29 can be demount ably secured within the opening in bottom plate 26. The inner surfaces of the segments and pole piece members can be aligned so as to provide finger 29 with a smooth walled inner bore 32.

A permanent magnet assembly which is inserted within the bore 32 of finger 29 includes a stack of alternating permanent magnets 33 and pole piece discs 34. The permanent magnets 33 are in pairs and arranged such that adjacent magnets in the stack are polarized in opposite directions. The pole piece discs 34 are placed in intimate contact with the smooth wall of bore 32 and located in registry with the pole piece members 3 1, the innermost pole piece disc 34 fitting intimately within a central recess in pole piece member 31'.

The magnets 33 and pole piece discs 34 are centrally bored to receive a stud 35 which clamps the assembly together. An end plate 36 is carried on the stack and is mounted from the bottom plate 26 by screws 37 to hold the magnet assembly in position.

Disposed between the pole pieces 34 and centered about the finger 29 are the pumping elements 38 which upon energization thereof are adapted to initiate and maintain a glow discharge. Each pumping element 38 includes a pair of split-annular, spaced-apart reactive cathode plates 39 such as titanium. Each plate 39 is held in intimate contact to a respective pole piece member 31 by a plurality of rods in gripping pins (not shown), the rods passing through apertures in the pole piece members 31 and slots in the plates 39 (not shown). Alternatively, the pole piece members 31 may act as the cathode member or be clad with the cathode material (usually titanium). Other suitable reactive materials are well known in the art. Additionally, the plates 39 could 4 v be split into arc segments to facilitate assembly and removal.

Positioned between and insulated from the cathode plates 39 are a plurality of anode cells made of, for example, titanium or stainless steel with wall thickness of 0.015-0.25" thick, brazedor spot-welded together in the form of an annular member 40. Additionally, anode member 40 may be split into 180 arc segments to facilitate assembly and removal. The anode member. 40 is held such that the individual cell axes are substantially parallel to the lines of magnetic flux, and supported in spaced-apart relationship from the cathode plates 39 a three points about its periphery by brackets 41, as of titanium or stainless steel, spot-welded thereto at one end and at the other end to a tubular conductive spacer 42, as of stainless steel, mounted on an anode support rod 43, as of stainless steel. The spacers 42 may be apertured to allow gases trapped within the spaces between the spacers 42 and support rods 43 to easily escape during pump operation. The anode support rods .43 are anchored to the ceramic insulator 44 at one end which in turn is carried on bottom plate 26 and to an upper cross arm 45 at the upper end. An additional insulator 46 anchored between cross arm 45 and uppermost pole piece member 31 serves to hold the anode members in fixed position. If desired, sputter shields may extend c0- axially of and slightly spaced from the insulators 44 and 46. Thus, the rods 43 and spacers 42 are electrically insulated from the envelope 24 and cathode; plates 39. A high, positive voltage, typically in the range of 2-l0 kilovolts, is applied to the anode memberv 40 with respect to the cathode plates 39 via the intermediary of a high voltage feedthrough 47, passing through the envelope 24, a conductivestrap 48, a spacer 42.0n one of the rods 43 and bracket 41.

In the case of some magnetically confined glow discharge pumps, it is desirable to cool the pump elements, in particular, the cathode. Such a pump is disclosed in US. Patent No. 3,149,774 issued Sept. 22, 1964 and assigned to the same assignee as the present invention. In the present invention this may be accomplished by flowing a coolant fluid such as air, water or refrigerant (such as liquid nitrogen) through a fluid conduit 49 brazed to the edges of pole pieces 31. The ends of conduit 49 pass through the envelope 24 via a coolant feedthrough 50 and are connected to an external coolant source (not shown).

In another embodiment of the present invention, as best seen in FIG. 4, magnetic ring segments 31a having the same outside diameter as tubular segments 30 are brazed between tubular segments 30. Annular pole pieces 31b extend outwardly of the finger and are located in registry with segments 31a beingheld by magnetic attracton. The use of segments 31a and annular pieces 31b instead of an integral pole piece member 31 as in the embodiment of FIGS. 2 and 3 facilitates assembly and stacking within the region of space to be evacuated.

Many changes can be made in the above construction and many apparently widely different embodiments of this invention can be made without departing from the scope thereof. For example, geometries other than circular can be employed, such as square and rectangular. More than one row of anode cells can be employed. Itis intended, therefore, that all matter contained in the above descrip tion or shown in the accompanying drawing shall be in terpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a magnetically confined glow discharge apparatus containing a region of space to be evacuated, the improvement comprising a gas impervious envelope having a wall forming said region of space to be evacuated, the wall of said envelope including a plurality of magnetic pole piece members and a non-magnetic, spacer segment located between said pole pieces members and serving to space said pole pieces members one from another, a magnet positioned externally of said envelope Wall with its north and south poles respectively positioned adjacent the pole piece members which are separated by said nonmagnetic spacer segment, said magnet being a separate element removable from said envelope wall, an anode member positioned inside said envelope, and said pole piece members having magnetic portions inside said envelope and positioned on opposite sides of said anode member.

2. The improvement according to claim 1 including a second magnet removably positioned externally of said envelope wall and having its south pole adjacent the south pole of said first magnet, a pole piece disc disposed externally of said envelope in intimate contact with said envelope wall located between said magnets in registry with one of said pole piece members and serving to space said magnets and provide a low reluctance path to said pole piece members.

3. The improvement according to claim 1 including reactive metal members disposed on opposite sides of said anode member and secured to said pole piece portions.

4. A magnetically confined glow discharge apparatus for evacuating a region of space, including: a gas impervious tube having a walled internal bore therein adapted and arranged to extend into the region to be evacuated, the wall of said tube including a plurality of pole piece members and a non-magnetic, tubular, spacer segment located between said pole piece members and serving to space said pole piece members one from another; magnet means telescopically received within said tube, including at least one pair of permanent magnets, each having a north pole at one end and a south pole at an opposite end, and arranged in a stack such that adjacent magnets in the stack are polarized in opposite directions; a plurality of pole piece discs disposed within said tube in intimate c0ntact with said walls, located between said permanent magnets in registry with said pole piece members and serving to space said permanent magnets and provide a low reluctance path to said pole piece members; said pole piece members including portions extending into said region to be evacuated; and an anode member adapted to initiate and maintain a glow discharge upon energization thereof, located within said region of space to be evacuated between said pole piece portions.

5. The improvement according to claim 4 wherein said tube has an open end large enough to permit insertion and removal of said magnets.

6. The improvement according to claim 4 wherein said tube has an open end large eough to permit insertion and removal of said magnets and said pole piece discs, and connecting means securing said magnets and pole piece discs together for insertion and removal as a unit.

7. The improvement according to claim 4 wherein said pole piece portions extending into said region of space comprise annular pole pieces dimensioned to encompass the wall of said tube in intimate contact therewith and separable therefrom.

8. The improvement according to claim 1 wherein said magnetic pole piece portions inside the envelope on 0pposite sides of the anode member are separate magnetic pieces abutting said pole piece members.

References Cited UNITED STATES PATENTS 3,144,200 8/1964 Taylor 23 069 3,216,652 11/1965 Knauer 313-7 X 3,231,175 1/1966 Zaphiropoulos 230l9 3,236,442 2/ 1966 Davis 230-69 DAVID J. GALVIN, Primary Examiner.

STANLEY D. SCHLOSSER, JAMES W. LAWRENCE,

Examiners.

S. A. SCHNEEBERGER, Assistant Examiner. 

